Known compounds having the same skeleton as the compound of the above-described formula (I) include antihypertensive compounds represented by the formula (II): ##STR2## wherein R.sub.1 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms; n represents 1 or 2; and R.sub.2 and R.sub.3, being different from each other, each represents a hydrogen atom, a chlorine atom, a bromine atom, a fluorine atom, a fluoromethyl group, a sulfonic acid group, a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a nitro group, an amino group or a phenyl group; or R.sub.2 and R.sub.3, being the same, each represents a hydrogen atom, a chlorine atom, a bromine atom, a fluorine atom, a hydroxyl group, an alkyl group having 1 to 3 carbon atoms or an alkoxyl group having 1 to 3 carbon atoms; or R.sub.2 and R.sub.3, being taken together, form a methyleneoxy group or a condensed benzene ring,
as disclosed in U.S. Pat. No. 3,932,407 corresponding to Japanese Patent Publication No. 23994/81. The abovementioned U.S Patent reported that these compounds exhibit a blood platelet aggregation inhibitory activity in addition to the antihypertensive activity.
However, among the above-described known compounds of the formula (II), those having excellent anti-platelet aggregation activity are all sparingly soluble in water and are not, therefore, suitable for parenteral administration. Further, these compounds (II) are characterized by their potent hypotensive activity, and such a hypotensive activity rather exerts a harmful influence on the circulatory system when applied in the therapy of thromboembolia making use of their platelet aggregation inhibitory activity.
Also, U.S. Pat. No. 4,256,748 discloses imidazo[2,1-b]quinazolin-2(3H)-ones which are useful for treating and prophylaxis of cardiac insufficiency and cardiac failure, but these compounds have a substituent such as an alkyl group at the 3-position of the imidazo[2,1-b]quinazolin skeleton and their activity is different from that of the compound of this invention.